I'm just finishing MM9, in the final area. I haven't managed to complete any artifact set, however while looking around I found this

http://www.zimlab.com/wizardry/recovered/flamestryke/mm9/items9/gatheringprizeset.html

"This set of items can be won at the fair known as the Gathering. The items are not very helpful, but you can sell the complete set to the Collector for a hefty premium."

Who is this "Collector" that the website is mentioning? Is there any one to whom you can sell complete artifact sets for a bigger prize?

It isn't artifact set, just some items from competition (I think it is similar to MM6 circus).

Actual artifacts come from black chests, like the one behind that powerful dragon (which seems to be the only dragon in this game).

Yes, I know that. But my question is regarding the text on that page.

"This set of items can be won at the fair known as the Gathering. The items are not very helpful, but you can sell the complete set to the Collector for a hefty premium."

It seems to indicate that there is a person in the game who will buy complete sets of artifacts, and among them, the Gathering prize set. It's just that I'm almost at the end of the game, and I haven't encountered such a person.